The action, which came as two Fairfax County supervisors switched their votes, clears the way to use a federal earmark for the first of three widening projects on I-66. But the rest of the project remains unfunded and probably is years from bringing relief to motorists.

The move reversed a decision by the National Capital Region Transportation Planning Board last month to strip the $75 million project from the region's transportation plan. Yesterday, the swing votes were cast by two Fairfax County supervisors, Catherine M. Hudgins (D-Hunter Mill) and Linda Q. Smyth (D-Providence), who last month had voted against the project.

In exchange, the Virginia Department of Transportation assured the board that no further funding for the I-66 project beyond the first phase would be committed until several studies are completed. But, as some board members pointed out, that is not much of a concession, because the state does not have money to fund the other two phases of the project anyway.

The I-66 project would connect a series of acceleration and deceleration lanes, effectively widening the westbound highway from two lanes to three between Fairfax Drive and Sycamore Street and from three lanes to four between Washington Boulevard and the Dulles Access Road. The first phase of the widening, from Fairfax Drive to Sycamore Street, was scheduled to start next year. It was funded by a congressional earmark sponsored by U.S. Rep. Frank R. Wolf (R) and former congressman Tom Davis (R).

The studies would look at requiring vehicles to carry at least three people to use the roadway's carpool lanes instead of the current two; introducing tolls and congestion pricing; increasing transit in the corridor; and additional roadway improvements both inside and outside the Beltway. Some parts of the study could take as long as a decade, VDOT officials said.

But Virginia Transportation Secretary Pierce R. Homer, in a letter to the board, said the first part of the study on transit alternatives would be presented to the board by the end of the year.

Hudgins and Smyth said the agreement, which passed on a voice vote, would ensure that VDOT keeps its word in studying alternatives to building more road capacity. They noted that the state promised to look at alternatives when the widening project was first approved two years ago.

"This just brings us back to where we were in 2007," Hudgins said.

David Snyder, a Falls Church City Council member who serves on the board, said the compromise was a "victory for good government" and would force VDOT to follow through with its promise for more study.

Fairfax County leaders said that the county is strongly in favor of the project and that its representatives to the regional panel had been told to change their votes.

But Fairfax County Supervisor Pat S. Herrity (R-Springfield) complained that the vote does not do what the county board had agreed to: commit funding for the entire project.

"We want all three [phases] back in without conditions," Herrity said. "This project has been studied to death."

Transportation board member Jonathan L. Way (R), a Manassas City Council member, offered an amendment that would have returned all three phases to the plan. It was defeated.

Pro-transit groups and Arlington County residents, who have long opposed the widening, said reviving it was a bad move.

"For years we have been saying, 'Wiser, not wider,' " said Peter Harnik of the Maywood Community Association in Arlington. "The board's vote last month showed you agree with this approach and we think it still holds today. If you reverse yourselves today, you'll be voting for ready, fire, aim."